Many ophthalmic formulations comprise compounds that provide lubricity and other desirable properties. When these formulations are instilled in the eye, the properties of such compounds can prevent undesirable problems such as bioadhesion and the formation of friction-induced tissue damage, as well as encourage the natural healing and restoration of previously damaged tissues.
Many marketed artificial tear solution products contain polymers that display thixotropic and viscoelastic properties. Some of these polymers include hydroxypropylmethylcellulose, galactomannans such as guar and hydroxypropyl guar, carboxymethylcellulose, hyaluronic acid, and sodium alginate. The shear thinning and viscoelastic profiles of polymers play important roles when mixed with the tear film.
The retention profile, lubrication and mucomimetic properties of polymers in artificial tear solution products may play an important role by to helping stabilize the tear film and providing improved comfort to patients with dry eye disease. For example, the product Systane® (Alcon, Inc.) containing hydroxypropyl guar and the active ingredients polyethylene glycol 400 and propylene glycol has been reported by Paugh, et al. (2008) to be more effective at eliminating eye discomfort than similar viscosity enhancing polymers such as carboxymethyl cellulose.
The bulk rheology of polymers used in artificial tear solutions is often characterized by steady state shear (shear thinning) and dynamic oscillation tests (viscoelasticity). Although these tests are valuable, these bulk rheology experiments may not fully characterize the interfacial properties of such polymers. An understanding of the polymers' interfacial properties is critical, as these properties may play important roles in the interactions with tear film components at both the cornea/tear film interface and tear film/air interface. Another rheology test that can aid in understanding the dynamic and interfacial properties of polymers used in artificial tears is the oscillation drop experiment, described herein.
Ophthalmic formulations have been previously described that utilize galactomannan-borate gelling systems. U.S. Pat. No. 6,403,609 to Asgharian, entitled “Ophthalmic compositions containing galactomannan polymers and borate,” describes such systems and is herein incorporated by reference in its entirety. The cross-linking of galactomannan and borate is responsible for the gel-forming behavior of the described formulations.